Notch signaling is an evolutionarily conserved pathway that regulates a diverse set of biological functions including stem cell maintenance, cell differentiation and proliferation in both embryonic development and adult tissues (Kopan et al., (2009) Cell 137: 216-233, Guruharsha et al., (2012) Nat Rev Genet. 13: 654-66, and Andersson et al., (2001) Development 138: 3593-3612). In mammals, four Notch receptors have been described (Notch1-4), which have a conserved domain architecture. The extracellular domain (ECD) consists of a series of EGF-like repeats followed by a negative regulatory region (NRR) which contains 3 Lin Notch Repeat (LNR) repeats and a heterodimerization domain. Canonical Notch signaling is activated when a Notch receptor on one cell interacts with a ligand on a neighboring cell. In mammals there are five trans-membrane ligands, three Delta-like ligands (DLL1, DLL4, and DLL3) and two Jagged ligands (Jagged1, Jagged2). Ligand binding results in cleavage of Notch by ADAM proteases at the S2 site within the NRR domain. This initial cleavage generates the substrate for subsequent cleavage of the Notch receptor at the S3 site by the γ-secretase complex. Following γ-secretase cleavage, the intracellular domain of Notch (ICD) translocates to the nucleus where it interacts with a CSL transcription factor (CBF-1/RBP-Jk in mammals) and the co-activator mastermind (MAML1) to activate target gene transcription. The HES/HEY family of transcription factors are well-characterized Notch target genes, however a large number of transcriptional targets are cell-type specific.
To date, the evidence for Notch receptors in cancer has focused primarily on alterations in Notch1 signaling, but very little on other Notch receptors. Accordingly, a need exists to study and identify methods and compositions that alter other Notch receptor signaling, such as Notch 3 signaling.